Means for treating foodstuffs



y 29, 1952 P. L. SPENCER 2,605,383

MEANS FOR TREATING FOODSTUFFS Original Filed Oct. 8, 1945 MA GNE TRON I G) r CONVEYOR s VSTEM M AG N E TQO N OSC/LLATO/Z 25 //v VEN 7'0]? ATTORNEY Patented July 29, 1952 UNITED STATES om cs Y I MEANS FOR- IREA'I'ING rooDsirUFFs Percy L. S encer, West Newton, Mass, assignmto Raytheon Manufacturing Company, Newton, Mass a corporation of Delaware Original application October 8, 1945, Serial No. 620,919. Divided and this application February 24,1947, Serial No. 730,600

'4 Claims. (01. 21947 This application is a division of my copending application, Ser. No. 6'20,9l9,flled October 8, 1945, now'Patent'No. 2,495,429.

My present invention relates to the treatment of foodstuffs, and more particularly to the cooking thereof through the use of electromagnetic energy.

Such energy has been used before for this purpose, but the frequencies employed have been relatively low, for example, not over 50 megacycles. I have found that, at frequencies of this order of magnitude, the energy necessarily expended in order to generate sufficient heat to satisfactorily cook the foodstuffs is much too high to permit the practical use of the process. I have further found, however, that this disadvantage may be eliminated by employing wave lengths fallin in the microwave region of the electromagnetic spectrum, for example, wave lengths of the order of 10 centimeters or less. By so doing, the wave length of the energy vbe comes comparable to the average dimension of the foodstuff to be cooked, and, as a result, the heat generated in the foodstuff becomes intense, the energy expended becomes a minimum, and the entire process becomes efficient and commercially feasible.

It therefore, one of the objects of my present invention to provide an efficient method of employing electromagnetic energy for the cookins of foodstuffs.

"It is a further object of my present invention to provide simple and inexpensive apparatus for carrying out such a cooking method.

In the accompanying specification I shall describe, and in the annexed drawing show, an illustrative embodiment of the method and means for treating foodstuffs of my present invention. It is, however, to be clearly understood that I do not wish to be limited to the details herein shown and described for purposes of illustration only, inasmuch as changes therein may be made without the exercise of the invention and within the true spirit and scope of the claims hereto appended.

In said drawing, the single figure is a schematic arrangement of apparatus which may be utilized to carry out the method of my present invention.

Referring now more in detail to the aforesaid illustrative embodiment of my present invention, with particular reference to the drawing illustrating the same, the numerals I and II generally designate electron-discharge devices of the magnetron type, each including, for example, an evacuated envelope It, made of highly conductive material, such as copper, and provided with a plurality of inwardly-directed, radially-disposed anode vanes IS. The arrangement is such that each pair of adjacent anode vanes I3 forms, together with that portion of the envelope l2 lying therebetween, a cavity resonator whose natural resonant frequency is, as is well known to those skilled in the art, a function of the geometry of the physical elements making up the same. For the purposes of my present invention it i desirable that the dimensions of each such cavity resonator be such that the wave length of the electrical oscillations adapted to be generated therein i comparable to the average dimension of the foodstuff to be cooked, for example, of the order of 10 centimeters or less.

Centrally located in each envelope I2 is a highly electron-emissive cathode member II, for example, of the well-known alkaline-earth metal oxide type, said cathode member being provided with conventional means (not shown) for raising the temperature thereof to a level sumclent for thermionic emission.

Each electron-discharge device it is completed by magnetic means (not shown) for establishing a magnetic field in a direction transversely of the electron path between the cathode and anode members thereof.

The conductive envelopes l2 of the electrondisch'ar'ge devices l0 and ll are connected, respectively, by conductors l5 and [6, to the opposite terminals of the secondary winding i1 01' a transformer It, the primary winding IQ of said transformer being connected to a source of raw A.-C., for example, the conventional 60-cycle power lines. The cathodes IA of said electrondischarge devices I0 and II are tied together by conductors 20 and H, which are, in turn, connected, by a conductor 22, to a center tap on the secondary winding ll of the transformer l8.

Thus, the electron-discharge devices l0 and II are connected for a push-pull operation, whereby said devices alternately deliver hyperfrequency energy to a common, hollow wave guide 23 through coaxial transmission lines 24 and 25 which are coupled to their respective oscillators, for example, by loops 2B and 21. By utilizing a pair of magnetrons connected in the manner disclosed across an alternating current source, I am able to more efficiently utilize the energy of the source, thus effectively obtaining a higher output from said source, since each magnetron will be operative through the half cycle of the alternat ing current source during which its anode is positive with respect to its cathode.

Adjacent the outlet end of the wave guide 23 I provide an appropriate, transversely-moving conveyor system 28 for carrying the foodstuff to be cooked into a region where it will be exposed to the energy emanating from said wave guide. The speed of the conveyor system is made such that, taking into account the nature of the particular foodstuff to be cooked, the time required for cooking the same, and the power of the wave energy emanating from guide 23, as well as the length parallel to the movement of the conveyor system of the opening in guide 23, the foodstufi carried by said conveyor system will be complete- 13! cooked during its travel past the open end of waveguide 23.

With the system described, I have found that an egg may be rendered hardboiled with the expenditure of 2 kw.-sec. This compares with an expenditure of 36 kw.-sec. to conventionally cook the same. I have also found that with my system a .potato requires theexpenditure of about 240 kw.-sec., which compares with 72,000 kw.-sec. necessary to cake the same in an electric oven. These examples are, it is to be clearly understood, merely illustrative. I have observed similar results with other foodstuffs. In each instance, where the wave length of the energy is of the order of the average dimension of the foodstuff to be cooked, the process is very efficient, requiring the expenditure of a minimum amount of energy for a minimum amount of time.

This completes the description of the aforesaid illustrative embodiment of my present inven tion. It will be noted from all of the foregoing that my process is simple and easily practiced; it is economical; and it requires relatively simple and inexpensive equipment.

Other objects and advantages or" my present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

1. A microwave power source comprising a pair of cavity magnetron oscillators, a source of alternating current, means connecting the inputs of said magnetron oscillators in push-pull to said alternating current source, and means coupling the outputs of said magnetron oscillators to a common load, said load comprisnig means for concentrating and guiding said energy from said magnetron oscillators toward and into the region of foodstuff with sufficient intensity to raise said foodstuff to cooking temperature.

2. A microwave power source comprising a pair of cavity magnetron oscillators, a source of alternating current, means connecting the inputs of said magnetron oscillators in pushpull to said alternating current source comprising means connecting the anodes of said magnetrons respectively to terminals of opposite polarity of said alternating current source, and means coupling the outputs of said magnetron oscillators to a common load, said load com prising means for concentrating and guiding said energy from said magnetron oscillators toward and. into the region of foodstuff with sufiicient intensity to raise said foodstuff to cooking temperature.

3. A microwave power source comprising a pair of microwave magnetron oscillators, a source of alternating current, means connecting the inputs of said magnetron oscillators in push-pull to said alternating current source, means coupling the outputs of said magnetron oscillators to a common load, said load comprising means for concentrating and guiding said energy from said magnetron oscillators toward and into the region of foodstuff with sufiicient intensity to raise said foodstuff to cooking temperature, and means for conveying said foodstuff through said region at such a rate of speed as to cook the same to a predetermined degree.

4. Apparatus for treating foodstufi comprising. a microwave power source comprising a pair of cavity magnetron oscillators, a source of alternating current, means connecting the inputs of said magnetron oscillators in push-pull substantially directly to said alternating current source, and means coupling the outputs of said magnetron oscillators to a common load, said load comprising means for concentrating and guiding said energy from said magnetron oscillators toward and into the region of said foodstuff with sufiicient intensity to raise said foodstuff to cooking temperature.

PERCY L. SPENCER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,751,485 Logwood Mar. 25, 1930 1,853,222 Hoermann June 14, 1932 1,900,573 McArthur Mar. 7, 1933 1,945,867 Rawls Feb. 6, 1934 1,981,583 Craig Nov. 20, 1934 2,092,227 Smith Sept. 7, 1937 2,103,362 Hansell Dec. 28, 1937 2,143,469 Smith Jan. 10, 1939 2,270,160 Berger Jan. 13, 1942 2,364,526 Hanseil Dec; 5, 1944 2,370,161 Hansen Feb. 27, 1945 2,390,572 De Brabander Dec. 11, 1945 2,391,085 Crandell Dec. 18, 1945 2,391,546 Chodorow Dec. 25, 1945 2,398,606 Wang Apr. 16, 1946 2,415,799 Reifel et al Feb. 11, 1947 2,427,094 Evans Sept. 9, 1947 2,433,067 Russell Dec. 23, 1947 2,436,732 Rowe T Feb. 24, 1948 2,448,527 Hanseil Sept. 7, 1948 2,474,938 Gorn July 5, 1949 2,495,429 Spencer Jan. 24, 1950 2,495,435 Welch Jan, 24, 1950 2,495,514 Marshall Jan. 24, 1950 2,500,752 Hanson et a1 Mar. 14, 1950 2,543,387 Brown et al. Mar. 6, 1951 OTHER REFERENCES Hutcheson, The Welding Engineer, December 1945, page 90.

Terman, Radio Engineering, third edition, 1947, page 3. 

